1. Data Flow Diagrams (DFDs)

2. Data flow diagram (DFD) is a picture of the movement of data between external entities and the processes and data stores within a system

3. DFD Symbols Process Data Flow Data Store Source/Sink (External Entity)

4. Process Work or actions performed on data (inside the system) Labels should be action phrases Receives input data and produces output

5. Rule 1: Process Can have more than one outgoing data flow or more than one incoming data flow

6. Rule 2: Process Can connect to any other symbol (including another process symbol)

7. Process: Correct/Incorrect?

8. Data Flow Is a path for data to move from one part of the IS to another Arrows depicting movement of data Can represent flow between process and data store by two separate arrows

9. Data Flow: Correct/Incorrect?

10. Data Store Is used in a DFD to represent data that the system stores Labels should be name phrases

11. Rule: Data Store Must have at least one incoming and one outgoing data flow

12. Data Store: Correct/Incorrect?

13. Source/Sink (External Entity) External entity that is origin or destination of data (outside the system) Is the singular form of a department, outside organisation, other IS, or person Labels should be noun phrases Source – Entity that supplies data to the system Sink – Entity that receives data from the system

14. Rule: Source/Sink Must be connected to a process by a data flow

15. Source/Sink: Correct/Incorrect?

16. Rules for Using DFD Symbols Data Flow That Connects YESNO A process to another process A process to an external entity A process to a data store An external entity to another external entity An external entity to a data store A data store to another data store

17. Context Diagram Top-level view of IS Shows the system boundaries, external entities that interact with the system, and major information flows between entities and the system. Example: Order system that a company uses to enter orders and apply payments against a customer’s balance

18. Context Diagram of Order System

19. Level-0 DFD Shows the system’s major processes, data flows, and data stores at a high level of abstraction When the Context Diagram is expanded into DFD level-0, all the connections that flow into and out of process 0 needs to be retained.

20. Context Diagram of Order System

21. Level-0 DFD of Order System

22. Lower-Level Diagrams Functional Decomposition – An iterative process of breaking a system description down into finer and finer detail – Uses a series of increasingly detailed DFDs to describe an IS Balancing – The conservation of inputs and outputs to a data flow process when that process is decomposed to a lower level – Ensures that the input and output data flows of the parent DFD are maintained on the child DFD

23. Strategies for Developing DFDs Top-down strategy – Create the high-level diagrams (Context Diagram), then low-level diagrams (Level-0 diagram), and so on Bottom-up strategy – Create the low-level diagrams, then higher-level diagrams

24. Identify Entities,Process,Data Stores & Data Flow Entities – Customer – Warehouse – Accounting Processes – 1.0 Check Status – 2.0 Issue Status Messages – 3.0 Generate Shipping Order – 4.0 Manage Accounts Receivable – 5.0 Produce Reports Data Stores – D1 Pending Orders – D2 Accounts Receivable Data Flows  Order  In-Stock Request  Order Data  Status Data  Status Message  Shipping Order  Order Data  Invoice  Shipping Confirmation  Payment  Accounting Data  Accounts Receivable Data  Order Data  Inventory Reports 1.0 2.0 3.0 4.0 5.0

25. Context Diagram of Order System

26. Level-0 of Order System